Authorities announced the arrest Thursday of the son-in-law of a couple who died as the result of a bomb explosion at their home just outside of Lebanon earlier this week.

Richard Parker, 49, was arrested at his home, adjacent to the home of his in-laws, the late Jon and Marion Setzer. Parker and his wife, Laura, the couple’s daughter, resided at 576 Vance Lane, and the Setzers resided at 580 Vance Lane.

Wilson County Sheriff Robert Bryan noted that the collaborative efforts of all the agencies involved in the investigation led to the arrest of Parker.

Mark Gwyn, director of the Tennessee Bureau of Investigation, said at approximately 4 p.m., Thursday, a special Wilson County grand jury was impaneled to evidence in the case and returned indictments against Parker. He is charged with two counts of felony first-degree murder, two counts of premeditated first-degree murder and one count of unlawful possession of a prohibited weapon. He was booked into the Wilson County Jail, and his bond was set at $1 million.

Jeff Fulton, special agent in charge with the Bureau of Alcohol, Tobacco, Firearms and Explosives, or ATF, said the investigation is continuing and the reward of $8,000 is still available.

“We still want the public’s assistance,” he said, asking for any additional evidence the public may have pertaining to this case.

He also confirmed, as did Michael Knight, public information officer with ATF, in an article about the bombing that will be published in the print edition of The Wilson Post on Friday that the bomb was not mailed.

“This device was placed,” Fulton said.

Dewey Woody, director of the Tennessee State Fire Marshal’s Office Bomb and Arson Unit, said from the beginning of the investigation that public safety was paramount and that remains the case.

“A lot of time was spent to discuss (the case),” he said, adding that he and other authorities appreciated the patience of the public.

He also added, “It is still an ongoing investigation.”

There remain many questions, such as how Parker was developed as a suspect, what was the motive for the crime and more, but Gwyn noted “We cannot go into the particulars of this investigation.”

He added that investigators received different leads and those along with evidence were taken into consideration. “We ran with it and it led us to Mr. Parker.”

Fulton noted that the components of the bomb were sent to labs – ATF’s and TBI’s – where they are still being analyzed.

“It was clearly a … destructive device,” he said.

Late Thursday afternoon, a news release from TBI noted that Parker was convicted of one count of arson in Giles County in 1993. He was given four years of probation for that crime.

Gwyn also added that authorities “would be remiss if we did not send out our condolences to the Setzer family” even though the circumstances were not what they wanted to hear. Mr. Setzer was pronounced dead at the scene of the incident on Monday. Mrs. Setzer reportedly was burned on more than 60 percent of her body and was transported by LifeFlight helicopter to Vanderbilt University Medical Center. She died Wednesday night.

“We feel like we have the person responsible for committing this crime in custody,” the TBI director said.